The solar cells present in conventional solar modules are typically embedded in a polymer material in order to protect them from environmental influences. The embedded solar cells are usually disposed between an upper glass layer and a backside layer, consisting of glass (double glass modules) or of a sealing film (glass-film modules). The material for embedding the solar cells is typically ethylene-vinyl acetate (EVA), which is used in the form of a film. Overall, customary polymers used for embedding of solar cells (EVA, PVB, polyolefins) have only low UV stability and have to be protected from the harmful effects of UV radiation by means of UV absorber substances. As a result, however, some of the light (up to 3%) is lost unutilized. More particularly, for novel cell concepts such as selective emitter cells, it is essential to be able to better exploit this component of light than is possible with conventional embedding materials.
There exist only a few inherently UV-stable polymers which do not need these protective absorbers. One example of such inherently UV-stable polymers are silicones. Three-dimensionally crosslinked silicone elastomers additionally have very good thermomechanical properties which make them suitable for the encapsulation of solar cells. For instance, the glass transition point is below −40° C. and they generally exhibit a small change in the mechanical properties with temperature.
However, these materials can be processed only in liquid form, more particularly as addition-crosslinking 2-component materials (liquid encapsulation). This involves bonding the two components, by means of an added catalyst, permanently to give a rubber-elastic polymer. The necessity of processing these materials in liquid form, however, complicates the use thereof in solar module construction, especially for mass production. A known liquid encapsulation process with liquid silicone is performed with an exceptionally slow-curing 2K system, by securing the cell matrix vertically between two glass plates, sealing the edges of the layup and slowly introducing the silicone from the bottom. However, this process is unsuitable for automated mass production with high throughput.
Other processes make use of horizontal encapsulation techniques, but these are problematic particularly with regard to the demands on the encapsulation material used. For example, DE 20 2010 005555 U1 describes a solar module and a production apparatus, wherein the solar module is produced with a bonding material for embedding of solar-active elements, which replaces the conventional EVA films. The bonding material described may have a pasty or liquid consistency and be cured after embedding. Examples mentioned for a suitable bonding material are silicone or silicone-containing compounds. DE 20 2010 005555 U1, however, does not mention the disadvantages and difficulties associated with the use of such liquid or pasty materials, nor does it disclose strategies by which these can be overcome.
There is therefore still a need for improved liquid encapsulation processes which partially or completely overcome the known disadvantages.